This is a continuing renewal application to follow this cohort at 5 to 7 years post-surgery. Important unanswered questions surround the long-term nature of body composition and resting energy expenditure (REE) after substantial and sustained weight loss by severely obese persons. This ancillary study cohort from LABS has been uniquely and comprehensively characterized for body composition and REE at T0 (before surgery), T12 (12 months post-surgery), and T24 (24 months post-surgery); therefore, it is well suited for further study of these same questions at ~T60 and T84 in that: they underwent massive weight loss; the weight loss was sustained at 24 months and is likely to be sustained over a long period of time thereby allowing for an investigation of whether adaptations of organ/tissue mass and fat redistribution occur; and REE relative to FFM at T24 continues to be lower compared to pre-surgery levels which is largely due to ongoing changes in organ mass. We propose to examine body composition and REE at the organ-tissue level at two additional time points, 60 months (T60) and 84 months (T84) post-surgery. We will continue to analyze the composition of body weight using the same advanced body composition models and measurement methods. MRI will describe body composition changes at the tissue/organ level and adipose tissue distribution allowing us to address questions of biological and clinical importance including the body composition changes' influences on REE. The specific aims are to: 1) measure important components of weight change in patients who underwent bariatric surgery on measures of fat mass and its distribution and FFM (including bone mineral density, skeletal muscle, and specific organs) at T60 and T84 months following surgery, and also to compare compartment sizes with those seen in stable weight controls; 2) measure the amount of change in REE at T60 and T84 compared to T0, following weight loss induced by bariatric surgery and to determine its relation to changes in body composition compartments, and its duration over the follow-up period. Secondary research questions relate to changes in cardiac structure and function, physical activity associations with skeletal muscle changes, and adipose tissue depot changes as predictors of cardiometabolic parameters (glucose metabolism and serum lipid composition). Consenting, eligible LABS patients previously enrolled in this ancillary study from Weill Cornell and the University of Pittsburgh will undergo the following measures: total body water by deuterium dilution (fat and FFM), extracellular water by sodium bromide tracer, body density by the BodPod, whole-body MRI (adipose tissue and its distribution; skeletal muscle mass; mass of liver, kidneys, heart, and brain), dual energy-X-ray absorptiometry (femur BMD, total body fat, fat-free mass, and bone mineral content), and REE. Subjects will be a women and men (n=100) equally distributed between the New York and Pittsburgh sites.